Groundbreaking CRISPR treatment for blindness only works for subset of patients

After some early but cautious optimism, a company is shelving its pioneering gene-editing treatment for a rare inherited blindness disorder. Editas Medicine announced today the trial trying to use the gene editor CRISPR to treat Leber congenital amaurosis 10 (LCA10) led to “clinically meaningful” vision improvements in only three of 14 patients.

In the study, patients received a subretinal injection of a modified virus carrying genetic material encoding components of CRISPR, a DNA-cleaving enzyme, and two RNA strands to guide the protein to its target sequences. For this trial, CRISPR was designed to snip out a problematic part of a gene called CEP290, which encodes a protein needed by the photoreceptor cells that eyes use to sense light. It was the first trial in the world to directly inject the gene-editing system into the body, rather than applying CRISPR to people’s cells in a lab dish and then reinfusing them.

Two of the patients whose vision improved—a woman treated early in the trial and a 14-year-old boy treated more recently, both of whom received midrange doses—had two defective copies...